Disk-based storage devices such as hard disk drives are used to provide non-volatile data storage in a wide variety of different types of data processing systems. A typical hard disk drive comprises a spindle that holds one or more flat circular storage disks, also referred to as platters. Each storage disk comprises a substrate made from a non-magnetic material, such as aluminum or glass, which is coated with one or more thin layers of magnetic material. In operation, data is read from and written to tracks of the storage disk via a read/write head that is moved precisely across the disk surface by a positioning arm as the disk spins at high speed.
Hard disk drive devices implement tunneling current sensor circuitry to detect when the read/write head is positioned at a proper distance from the storage disk to perform a read or write operation. A sensor element, which is manufactured as part of the read/write head, operates as a transducer that generates a sensor current as the read/write head approaches the storage disk. The sensor current output from the sensor element is processed by the tunneling current sensor circuitry to determine when the read/write head is properly positioned at a predetermined gap distance from the surface of the storage disk to perform a read or write operation, based on a magnitude of the sensor current.